1. Field of the Invention
The present invention relates to a hemocompatible polymeric resin functionalized to remove phosphate anions from whole blood without appreciably effecting the concentration of the other major anions of chloride and bicarbonate. The polymeric resin is targeted for extracorporal application in conjunction with hemodialysis. The functioning binding agent for the phosphate is a polyvalent cation attached to the polymer via an anionic group.
2. Description of Related Art
People with functioning kidneys have normal phosphate levels in their blood of 2.5 to 4.5 mg/dl of blood (measured as phosphorus), so that the phosphate anion concentration calculated as a millimole of HPO42− anion ranges within 0.081 to 0.145 mmole per dl (deciliter). At the pH of blood ranging from 7.35 to 7.45, the predominant monomeric phosphate anion is the monohydrogenphosphate anion, HPO42−. The phosphate anion level is held in this narrow concentration range for a healthy homeostasis by the normal functioning kidney via a check and balance system that involves hormones and reabsorption of water and electrolyte (ions) in the tubules of the kidney.
People with End Stage Renal Function or Disease are not able to keep the phosphate level in the blood within the proper normal range when eating a normal protein diet. Phosphate enters the body primarily through ingested protein. The phosphate level rises out of control with such individuals reaching blood levels as high as four times (4×) the normal blood concentration. This condition, known as hyperphosphatemia, if untreated allows calcium to be pulled from the bone mass producing degenerative bone disease.
For people with End Stage Renal Disease (ESRD), the phosphate concentration in the blood is regulated by either a low protein diet or by ingesting phosphate binders with the food intake. The phosphate anions from the ingested protein are trapped by the binder or sequestrant and are carried out with the feces with only a very small amount of absorption into the blood from the intestinal tract. The phosphate binders initially used were aluminum and calcium compounds, but these were found to have moderately severe to very severe side effects. More recently (1997–2004), phosphate binding agents have been developed that are anion exchange polymers (RenaGel® and a polymer bound guanidinium hydrochloride) and less toxic inorganic compounds such as lanthanum carbonate tetrahydrate (Fosrenal™), ferric salts of citrate and acetate, and a lanthanum based porous ceramic material (RenaZorb™). All of these phosphate-binding agents are ingested with food and are designed to sequester phosphate anions during the digestive process in the intestinal tract. The absorption through the intestinal wall into the blood by the bound or sequestered phosphate is hindered and, consequently, the phosphate is carried out by way of the feces.
This invention defines polymeric sequestrants for phosphate anions that are not ingested with food at mealtime. They function by binding phosphate anions directly from the blood as part of the hemodialysis system during the treatment sessions for people with End Stage Renal Disease (ESRD). These polymers function as selective sequestrants for the divalent monohydrogenphosphate anion and the anions of polyphosphoric acids without disturbing the concentrations of the other major anions of chloride and bicarbonate. Since bicarbonate is not bound by these sequestrants, the pH of the blood is unaltered during the treatment session.